Target screens for cathode ray tubes utilizing index generating materials that emit x-rays

ABSTRACT

Beam-index cathode ray tubes comprising target screens structured with index generating materials that emit X-rays which are detected to provide index signals indicative of the position of impact of the cathode rays on the screen. The screen is comprised of special X-ray emitting regions, including thin narrow strips in register with different color-producing phosphors. Embodiments are disclosed with and without an electron-transparent aluminum layer overlaying the phosphors and the index strips.

United States Patent Goodman [54] TARGET SCREENS FOR CATHODE RAY TUBESUTILIZING INDEX GENERATING MATERIALS THAT EMIT X-RAYS [72] Inventor:David M. Goodman, 3843 Debra Court, Seaford, NY. 11783 [22] Filed: Jan.27, 1961 [21] Appl. No.: 85,353

Related US. Application Data [62] Division of Ser. No. 800,854, March20, 1959,

Pat. No. 3,081,414.

52 us. c1 ..31s/21c,315/1o, l78/5.4, 313/92? 51 1111. C1 ..11013 29/70[58] Field of Search ..313/92, 92 P;'l78/5.4 AC; 315/21 c, 10

[56] References Cited UNITED STATES PATENTS 2,633,547 3/1953 Law..313/925 51 Sept. 12,1972

2,719,241 9/1955 Coltman ..313/92.5 X

Primary Examiner-Carl D. Quarforth Assistant Examiner-J. M. Potenza 57ABSTRACT Beam-index cathode ray tubes comprising target screensstructured with index generating materials that emit X-rays which aredetected to provide index signals indicative of the position of impactof the cathode rays on the screen. The screen is comprised of specialX-ray emitting regions, including thin narrow strips in register withdifi'erent color-producing phosphors. Embodiments are disclosed with andwithout an electron-transparent aluminum layer overlaying the phosphorsand the index strips.

7 Claims, 6 Drawing Figures PATENTEDSEP 12 I972 3.691.424

FIG. 1

k HI/J 36 r30 RG BGR R s as 38 40 I? 38 36 2'2 37 "ITMI- \TM TI+TZ+IFIG. 2 FIG. 2 FIG. 2

4,4 I 4 5 39 g8 2e 2 V2 R B e I Q 3 I FIG. 3

INVENTOR.

DAVID M. GOODMAN ATTORNEYS TARGET SCREENS FOR CATHODE RAY TUBESUTILIZING INDEX GENERATING MATERIALS THAT EMIT X-RAYS This inventionrelates to target screens for cathode ray tubes, and the like. It is adivision of my pending application Ser. No. 800,854, filed Mar. 20, 1059now U.S. Pat. No. 3,081,414 issued Mar. 12, 1963.

The use of index signals to signify the location of impact on the targetscreen of a scanning electron beam is recognized as a valuable tool inthe generation of cathode ray tube displays. Capacity effects, secondaryemission phenomena, and electro-magnetic radiation have been utilizedfor producing these index signals.

The primary object of this invention is to provide new and improvedmeans for generating index signals of the class comprised ofelectro-magnetic radiation.

Another object of this invention is to provide im-' proved means forproducing electro-magnetic radiation utilized at the target screen of adirected ray tube for purposes of examination or display.

Briefly stated, these objectives are achieved by purposely generatingX-rays when the electron beam of the cathode ray tube impinges uponindicia generating elements of the target screen. These X-rays, whichthus indicate the position of the electron beam on the target screen,are then filtered so that they are separated from the remainder of theradiations which may exist. The wide range of index signals that maythus be generated, the ease with which they can be filtered, their highspeed of transmission, and their rapid decay upon cessation ofexcitation comprise the main advantages in using X-rays for thispurpose.

Further advantages and objectives will become clear from the followingspecification taken in conjunction with the drawing wherein:

FIG. 1 represents a cathode ray tube with a target screen, index signalgenerating elements, and filter elements.

FIG. 2 represents a target screen configuration that may be used in thetube ofFIG. 1.

FIG. 2a illustrates a cross sectional view of the target screen of FIG.2.

FIG. 2b illustrates a mesh-like structure that may be used as a targetscreen.

FIG. 3 represents another target screen configuration that may be usedin the tube of FIG. 1.

FIG. 3a illustrates a cross sectional view of the target screen of FIG.3 with three different arrangements for generating index signals.

In FIG. 1, there is shown a cathode ray tube envelope containing anelectron beam forming member 12. Target screen assembly 14 is scanned bythe electron beam furnished by member 12. Two radiation detectors 18 areshown located external of the tube. They are X-ray responsive and aredisposed substantially parallel to and near the plane of the targetscreen assembly 14. Two radiation detectors 24 are shown disposed withinthe neck portion 26 of the cathode ray tube. Detectors 24 may be usedwith detectors 18, depending upon the total number of indexing signalsbeing generated as will become clear. The target screen assembly 14consists of members 28, 30, and 32. Member 28 in one embodiment, iscomprised of phosphors or other visible radiation emitting materialsarranged in narrow strips which are positioned lengthwise in thevertical direction. The horizontal scanning of these strips takes placesubstantially perpendicular to the thus designated vertical direction.Member 30 is an electron-transparent light-reflecting aluminum layer.Member 32 consists of strips that provide electro-magnetic indexradiation when bombarded by the scanning beam of electrons. Dependingupon the materialsthat these strips are made of, the electro-magneticindex radiation may extend from waves of infrared to X-rays. When thisindexing radiation is in the X- ray region, members 30 and 32 may beinterchanged, as will be explained infra. In FIG. 3a a target assemblyis shown which is capable of generating index signals in the Hertzianrange.

FIG. 2 shows, on an enlarged scale a front view of one possiblearrangement of layer 28 of target screen assembly 14. Red, green, andblue color producing phosphors are arranged in the sequence red-green,blue-green and are designated 40-41, 42-43. The dimensions of thephosphor strips that are selected for this purpose are such that whenthe horizontal scanning beam, which proceeds linearly from left to rightacross FIG. 2, is constant in intensity, a substantial white image ispresented to the observer. This is achieved by having the widths of thestrips in the path of scan inversely proportional to the luminousefficiencies of the color producing phosphors. Phosphors are presentlyavailable which are more efficient in the green than in the blue, whichis more efficient than the red. Therefore the red strip is widest, theblue strip is narrower, and the sum of the two green strips isnarrowest. The efficiencies stated are those which apply when a humanbeing is the observer. The green strip is divided as shown since thevisual acuity of the eye is greatest in the green region of thespectrum. For detectors other than the eye similar considerationsprevail. Strips 36 and 38 of which layer 32 is comprised, are deposited,or placed on the aluminum layer 30, or on the phosphor layer 28. Thesestrips provide the electromagnetic index signals. The signal from strip36 is used to excite, via suitable circuitry, the red-green phosphorcombination; the index signal from 38 is used to excite, via suitablecircuitry, the blue-green phosphor combination. The indexing strip is infront of the color producing strips with which it is associated so thatthe scanning time required for the beam to proceed from strip 36 tostrip 40 is substantially equal to the overall delay that is encounteredbetween the generation of the index signal at 36 and the time that itseffect is felt at strip 40. This time delay is shown in FIG. 2 as T,,,.An equal delay T,,, is shown to exist between the indexing strip 38 andcolor producing strip 42. For optimum performance the period T,,, shouldbe reduced to a minimum. This may be accomplished by using anelectro-magnetic radiation index signal and by using a minimum number ofwide band circuits.

In FIG. 2a there is a cross sectional view of one configuration of thescreen of FIG. 2. The color producing phosphor strips 40, 41, 42, 43 areillustrated. The layer 30 of electron-transparent aluminum is alsoshown. Indexing strips 36 and 38 are on the side of the screen intendedto face the gun of the tube, corresponding to layer 32 of FIG. 1. Strips36 may consist of suitably prepared Hex ZnO, or Ba SiQ, activated bylead, or by tri-clinic CaMgSiO, activated by Cerium. When bombarded bythe scanningbeam the strip 36 will produce electro-magnetic radiation inthe neighborhood of 3,700A. This radiation has the furthercharacteristic of decaying very rapidly upon cessation of energization.Strip 38 may consist of a tungsten wire, or molybdenum, or othermaterial with high atomic number that generates X-rays upon exciation bythe scanning beam. X-ray production is normally encountered when thescanning beam strikes layer 30, and the phosphor strips. It is made toincrease substantially when the beam strikes 38 due to the fact that theefficiency of X- ray production is proportional to the atomic number ofthe metal of which the target is constructed. The governing equationessentially is: efficiency 1.4 X l ZV where Z is the atomic number ofthe target, and V is the electron accelerating voltage. For tungsten, Z74, and at 20KV the efficiency is approximately 0.2 percent. ThisX-radiation also decays very rapidly after cessation of energization;more so than the phosphors of which strip 36 may consist. Hence thescreen of FIg. 2a may be used to generate two electro-magnetic indexsignals which are distinguishable from each other, from the visibledisplay, and from spurious radiations.

In the event that strip 36 also is preferred to be an X- ray emitterthan it is desirable to make use of the characteristic radiation of theX-ray producing strips. Molybdenum for example, operated at 20KV willyield characteristic radiation at 0.71 and 0.63A. By suitable filtering,in the detector or in the screen, it is possible to distinguish thecontinuous distribution of X-rays produced by the tungsten strip 36,from the characteristic radiation of molybdenum strip 38. If it isdesired to use a plurality of strips that emit characteristic radiationit is necessary to make a selection governed by Moseleys law f K (Z-6)which states that the frequency of the characteristic radiation isproportional to the atomic number of the emitter. For example, copperhas a K-radiation at 1.5 3A when excited by SKV electrons. At KV thisradiation increases much more rapidly than the background, or continuousradiation. The method of generating these characteristic spectra, and offiltering the separate radiations, is well known to those skilled in theuse of X-rays. I refer to X-Rays and Electrons by Arthur H. Compton,1926, published by D. Van Nostrand Company, and to X-Rays in Practise byWayne T. Sproull, published by McGraw Hill, 1946, tables III, IV, and V,for further particulars. Three points will be mentioned here forsimplifying the understanding of this facet of the invention. First, thecharacteristic radiation shows up as a sharp peak in the plot ofintensity versus wavelength for a particular target. Second, anexcitation energy which exceeds a certain minimum is required to excitethese peaks. Third, a material that is the same as the target materialused in generating characteristic spectra does not have a strongaffinity for absorbing such characteristic radiation.

In view of the importance of generating these signals alternate meansare illustrated in FIG. 2b, and in FIG. 3a. In FIG. 2b a mesh-likestructure is formed of horizontal members 37, and vertical members 36and 38. The interstices of this structure are filled, stripwise, withphosphors to provide the color producing strips 40, 41, 42, and 43.Member 36 may consist of a copper wire; member 38 may consist of amolybdenum wire; many other choices exist as was just explained.

The members 37 may or may not be conductive but should be substantiallydifferent from 36 or 38 insofar as X-ray producing qualities areconcerned. The conductive assembly is operated at high voltage. It isclear that as the electron beam scans from left to right indexingsignals will be generated. The overall time delay in the circuitry usingthese signals should be adjusted to T and T which represent periods oftime akin to T,, of FIG. 2.

In FIG. 3, a single indexing strip 44 is shown. The signals derived from44 will provide gating pulses for energization of the red, blue, andgreen phosphors. The overall time delay, between generating the indexsignal at 44 and energizing the first phosphor strip, is shown to be TAs was stated with respect to FIG. 2, it is desirable to reduce theoverall time delay to a minimum.

In FIG. 3a a cross section of a target screen configuration is shownwhich will provide three different electro-magnetic index signals.Phosphor layer 28 comprises strips of color emitting phosphors; layer 30is electron-transparent and light-reflecting; layer 32, alsoelectron-transparent, provides continuous X-radiation, and may alsoprovide characteristic X-radiation. A constant voltage V is maintainedat the side of the target screen opposite layer 32. A suitable voltage Vis maintained across layer 32. When the scanning beam of electronstraverses the layer 32, electro-magnetic index signals are generated at44a, 44b, and 440. The voltage V may be applied by means of atransparent electrical coating. This coating may be applied to member 28or to the faceplate of the tube to which it is to be positioned, oradhered. The voltage V may be applied via member 32.

The signal at 44a occurs in the following manner. Layer 32 is maintainedat 20KV and consists of a thin layer of copper for example. When 32 isscanned by 20KV electrons a continuous spectrum, and 15 3Acharacteristic radiation, are emitted. Either, or both, of these signalsmay be detected. The region 45 is maintained at V a voltagesubstantially different from V,. This may be accomplished by thetransparent coating or by placing a wire grid at 45. The faceplate oftube envelope 10 may also be used to provide the grid; or constructionas illustrated in my U. S. Pat. Nos. 2,885,591 and 2,897,388, may beused. Voltage V, may be at ground potential, or some other value lowerthan V thereby to produce radiation characteristics which are determinedby the deceleration of the electron beam. On the other hand, V may be ata voltage higher than V This is especially the case if it is desired togenerate characteristic radiation at element 45.

The signal at 44b occurs due to the removal of a strip of layer 32. Whenthe electron beam scans this region clearly a change in the X-radiationwill be produced which is detectable.

The signal at 440 also occurs due to acceleration or deceleration of theelectrons. However, the layer 32 is not altered as at 44a and 44b. Thismay be desirable for production purposes. When X-radiation is augmentedat 47 for indexing purposes in one of the manners previously set forth,it will be found that the thin, electron transparent layer 32, which isat 44c, will not materially attenuate these X-rays.

Another mode of operation of the target screen at 44c, and at 440,consists of regulating the velocity change of the electrons, and therate of the velocity change, to produce electro-magnetic signals in thel-lertzian and microwave range. The frequency of these signals iscontrolled by V V and the physical distance between them.

it is clear that the previous considerations relating to the generationand filtering of the X-ray index signals also apply when the indexsignal generating components are admixed with the color producingphosphors. The use of tungsten or molybdenum particles for this purposehas been described in my US. Pat. Nos. 2,885,591 and 2,897,388 mentionedabove.

Thus, a plurality of electro-magnetic index signals may be generatedthat indicate the position of a scanning beam on a directed ray tube.Many electromagnetic radiations may be used, it being clear that eachradiation may serve as a separate communication or control channel. Inthe case of radiation in the visible range optical techniques forfiltering the radiations are well known; in the microwave, orl-lertzian, range electrical filtering techniques are also well known;in the X-ray region techniques for producing and filtering monochromaticradiation are likewise well known. In addition to the Compton and Sproulreferences already cited, I also refer to Applied X-Rays, by Clark, Mc-Graw Hill, 1955. The wide range of signals that may be utilizedconstitutes one advantage of this invention. It is also to be noted thatthese teachings can be applied to storage-type devices, to signalgenerators, to quantizers, etc. In applications utilizing the scanningof a beam relative to a target where high speeds, high definition, wideband widths, and minimum distortions are required, this inventionprovides its greatest advantages.

Having thus described my invention, I claim:

1. A beam-index cathode ray tube with an electron gun for providing ascannable electron beam and a target screen comprising:

a first electron-sensitive fluorescent portion constructed and arrangedin a geometric configuration so as to emit radiant energy within a firstrange of wavelengths in response to excitation via a scanning action ofthe electron beam;

a second electron-sensitive portion constructed and arranged in arelated geometric configuration to emit radiant energy of a second rangeof wavelengths in the X-ray region of the spectrum, for indicating viaindex signals the position of impact of the electron beam;

and a layer of an electrically conductive electronpermeable materialdeposited on said first and second portions, said layer beingconstructed so as to transmit the radiant energy in the X-ray region;

in combination with index-signal producing means responsive to thetransmitted radiation in the X- ray region.

2. The combination of claim 1 wherein said indexsignal producing meanscomprises X-ray detection means positioned inside the tube andrearwardly of the target screen.

3. A beam-index cathode ray tube, used to reproduce images of scenestelevised in color, with an electron gun for providing a scannableelectron beam and a target screen comprising:

a first electron-sensitive fluorescent portion constructed and arrangedso as to emit light of selected colors in response to excitation via ascanning action of the electron beam;

a second electron-sensitive portion constructed and arranged so as toemit invisible radiation in the X- ray region of the spectrum, forindicating the position of impact of the electron beam;

and a layer of an electrically conductive and electron-permeablematerial deposited on said first and second portions, said layer beingconstructed so as to transmit the invisible X-radiation;

in combination with index signal producing means positioned rearwardlyof the target screen inside the tube so as to be impinged upon by saidinvisible X-radiation transmitted through said layer.

4. The combination of claim 3 wherein said first portion comprises aplurality of different color-producing phosphor strips configured in arepeating array,

and said second portion comprises a plurality of strips of X-rayemitting material in register with the color-producing phosphor strips.

5. In combination:

a beam-index cathode ray tube with an electron gun for providing ascannable electron beam and a target screen comprising:

a first plurality of electron-sensitive strip-like portions which emitradiant energy in response to excitation by the scannable electron beam;

and in registry therewith a second plurality of electron-sensitivestrip-like portions which emit X-rays in response to bombardment by theelectron beam thereby to indicate the position of impact on the targetscreen of the electron beam;

and index signal deriving means responsive to the intensity of saidX-rays for signalling the position of the electron beam;

wherein the strip-like X-ray emitting portions are comprised ofelectrically conductive material mounted in juxtaposition with saidfirst plurality of strip-like portions thereby to also provide theoperating voltage for the target screen.

6. The combination of claim 5 including electrically insulating strandsarranged in a mesh-like configuration with respect to the strips ofelectrically conductive material.

7. The combination of claim 5 wherein the first plurality of strip-likeportions comprises different colorproducing phosphors configured to forma repeating array of color-producing strips.

1. A beam-index cathode ray tube with an electron gun for providing ascannable electron beam and a target screen comprising: a firstelectron-sensitive fluorescent portion constructed and arranged in ageometric configuration so as to emit radiant energy within a firstrange of wavelengths in response to excitation via a scanning action ofthe electron beam; a second electron-sensitive portion constructed andarranged in a related geometric configuration to emit radiant energy ofa second range of wavelengths in the X-ray region of the spectrum, forindicating via index signals the position of impact of the electronbeam; and a layer of an electrically conductive electron-permeablematerial deposited on said first and second portions, said layer beingconstructed so as to transmit the radiant energy in the X-ray region; incombination with index-signal producing means responsive to thetransmitted radiation in the X-ray region.
 2. The combination of claim 1wherein said index-signal producing means comprises X-ray detectionmeans positioned inside the tube and rearwardly of the target screen. 3.A beam-index cathode ray tube, used to reproduce images of scenestelevised in color, with an electron gun for providing a scannableelectron beam and a target screen comprising: a first electron-sensitivefluorescent portion constructed and arranged so as to emit light ofselected colors in response to excitation via a scanning action of theelectron beam; a second electron-sensitive portion constructed andarranged so as to emit invisible radiation in the X-ray region of thespectrum, for indicating the position of impact of the electron beam;and a layer of an electrically conductive and electron-permeablematerial deposited on said first and second portions, said layer beingconstructed so as to transmit the invisible X-radiation; in combinationwith index signal producing means positioned rearwardly of the targetscreen inside the tube so as to be impinged upon by said invisibleX-radiation transmitted through said layer.
 4. The combination of claim3 wherein said first portion comprises a plurality of differentcolor-producing phosphor strips configured in a repeating array, andsaid second portion comprises a plurality of strips of X-ray emittingmaterial in register with the color-producing phosphor strips.
 5. Incombination: a beam-index cathode ray tube with an electron gun forproviding a scannable electron beam and a target screen comprising: afirst plurality of electron-sensitive strip-like portions which emitradiant energy in response to excitation by the scannable electron beam;and in registry therewith a second plurality of electron-sensitivestrip-like portions which emit X-rays in response to bombardment by theelectron beam thereby to indicate the position of impact on the targetscreen of the electron beam; and index signal deriving means responsiveto the intensity of said X-rays for signalling the position of theelectron beam; wherein the strip-like X-ray emitting portions arecomprised of electrically conductive material mounted in juxtapositionwith said first plurality of strip-like portions thereby to also providethe operating voltage for the target screen.
 6. The combination of claim5 including electrically insulating strands arranged in a mesh-likeconfiguration with respect to the strips of electrically conductivematerial.
 7. The combination of claim 5 wherein the first plurality ofstrip-like portions comprises different color-producing phosphorsconfigured to form a repeating array of color-producing strips.